I'm in Ohio. I drive interstate almost every day as well. I've driven to the surrounding states, driven taller and shorter vehicles, and have had my share of rocks thrown at the car from dump trucks, semis, etc, but never have had a cracked or broken windshield. Heck I had some dumb kid throw a large chunk of packed ice from a bridge while I was on the highway and while it scared the crap out of me when it hit (sounded like a bomb going off) the glass was still OK. I have had a couple rock chips, yes, but that's it.
Maybe you just keep getting cheap glass